Undesirable combustion characteristic detection apparatus

Abstract

An apparatus for detecting undesirable combustion characteristics in spark-ignited internal combustion engines. A sensor and a band-pass filter tuned to the frequency of the knock vibration are provided with an output of the band-pass filter being compared with a reference value. The result of the comparison is correlated with undesirable combustion characteristics to be recognized. A rectifier is provided for solid-borne sound signals received by the sensor with the signals passing through the band-pass filter. The signal is rectified in the rectifier to a knock signal and a series circuit made up of a band-stop filter tuned to the frequency of the knock vibration, an rms rectifier, and an amplifier is provided by means of which the sound signal received by the sensor is converted into a reference signal. A comparator is provided when the reference signal and the knock signal are compared with each other and an output signal appears if the knock signal exceeds the reference signal.

We claim: 
     
       1. Device for recognizing undesired combustion processes in internal combustion engines with conventional ignition systems by means of an acceleration sensor, a band-pass filter tuned to the frequency of the knocking vibrations, rectifiers located in the signal path of the knocking signal and of a reference signal path, and a comparator, whose output signal is assigned to the undesired combustion processes to be recognized, characterized by the fact that the band-pass filter is disposed with one rectifier in the signal path of the knocking signal and by the fact that in the signal path of the reference signal, there is a series circuit composed of a band elimination filter means tuned to the knocking frequency, a rectifier, and an amplifier, whereby the rectifier is an RMS rectifier and whereby the body noise signal is converted into the reference signal by the series circuit when it is received from the acceleration sensor. 
     
     
       2. An apparatus according to claim 1, characterized in that the reference signal path includes a band elimination filter means tuned to the frequency of the knock vibration and the RMS rectifier means is arranged in series with the band elimination filter means, and in that the output signal of the sensor means is fed to the band elimination filter means and an output signal from the band elimination filter means is fed to the RMS rectifier means. 
     
     
       3. An apparatus according to claim 2, characterized in that the reference signal path further includes an amplifier means for amplifying an output signal of the RMS rectifier means and for providing an output signal to the comparator means. 
     
     
       4. An apparatus according to claim 3, characterized in that the amplifier means is a linear amplifier. 
     
     
       5. An apparatus according to claim 3, characterized in that the amplifier means is a nonlinear amplifier. 
     
     
       6. An apparatus according to one of claims 2, 3, 4, 5 or 1 characterized in that an input amplifier means is disposed between the sensor means and the band-pass filter means and reference signal path for amplifying the output signal of the sensor means prior to an output signal being fed to the band-pass filter means and reference signal path.